(i) Technical Field of the Invention
The present invention relates to a ceramic-based composite member superior in hermetic properties and resistance to thermal shock and its manufacturing method.
(ii) Description of the Related Art
In order to raise performance of a rocket engine using NTO/N2H4, NTO/MMH, and the like as impelling agents, heat-resistant temperature of a combustor (thrust chamber) is requested to be raised. For this purpose, a coated niobium alloy having a heat-resistant temperature of about 1500xc2x0 C. has been heretofore used as a chamber material for many rocket engines. However, this material is disadvantageously heavy because of its high density, low in high-temperature strength, and has a short coating life.
On the other hand, since ceramic is high in heat resisting properties but disadvantageously brittle, a ceramic matrix composite member (hereinafter abbreviated as CMC) has been developed by reinforcing the ceramic with ceramic fiber. Specifically, a ceramic-based composite member (CMC) comprises ceramic fiber and ceramic matrix. Additionally, in general the CMC is indicated as ceramic fiber/ceramic matrix by its material (e.g., when both are formed of SiC, SiC/SiC is indicated).
Since CMC is light-weight and high in high-temperature strength, it is a remarkably prospective material for the combustor (thrust chamber) of the rocket engine, further a fuel piping in a high-temperature section, a turbine vane of a jet engine, a combustor, an after-burner component, and the like.
However, the conventional CMC cannot hold its hermetic properties and is disadvantageously low in resistance to thermal shock and thermal cycles. Specifically, for the conventional CMC, after a predetermined shape is formed of ceramic fibers, a matrix is formed in a gap between the fibers in so-called CVI (Chemical Vapor Infiltration) treatment. However, what remains a problem is that it takes an impractically long time (e.g., one year or more) to completely fill the gap between the fibers by the CVI.
Moreover, in a high-temperature test or the like of the conventional CMC formed as described above, when a fierce thermal shock (e.g., temperature difference of 900xc2x0 C. or more) acts, the strength is drastically lowered, and the CMC can hardly be reused.
Therefore, the conventional ceramic-based composite member (CMC) cannot substantially be used in the combustor (thrust chamber), the fuel piping or another component requiring the hermetic properties and resistance to thermal shock.
The present invention has been developed to solve the aforementioned problems. Specifically, an object of the present invention is to provide a ceramic-based composite member and its manufacturing method which can largely enhance hermetic properties and resistance to thermal shock and which can be for practical use in a thrust chamber and the like.
According to the present invention, there is provided a ceramic-based composite member comprising a dense matrix formed on a surface of a shaped fabric, and a matrix having fine cracks formed in a gap of the matrix.
In the structure, since the binding force of the ceramic fiber by the matrix having fine cracks is weak, a kind of soft structure is formed, Young""s modulus is lowered, the thermal stress is reduced, and the resistance to thermal shock is enhanced.
Moreover, according to the present invention, there is provided a method of manufacturing a ceramic-based composite member, in which after CVI treatment is performed to form an SiC matrix on a surface of a shaped fabric, PIP treatment is performed to infiltrate a gap of the dense matrix with an organic silicon polymer as a base before performing pyrolysis.
The method of the present invention is a process (hereinafter referred to as the hybrid treatment) constituted by combining CVI and PIP treatments, a dense matrix is formed around a ceramic fiber by CVI treatment, and the gap is infiltrated/filled with the matrix by the PIP treatment. Additionally, the matrix formed by the hybrid treatment is called the hybrid matrix.
The PIP (Polymer Impregnation and Pyrolysis) treatment has a faster matrix forming rate as compared with CVI treatment, and can repeatedly be performed in a short time. Therefore, by repeating the PIP treatment, the gap after the CVI treatment is filled well, and the hermetic properties can be enhanced.
Moreover, since fine cracks are present in the matrix by PIP treatment, a binding force of the ceramic fiber is weak. Therefore, when the PIP treatment is applied in addition to the CVI treatment, Young""s modulus can be reduced as compared with the conventional CMC only by CVI treatment, and, as a result, it has been confirmed by experiments that a thermal stress is alleviated and the resistance to thermal shock is remarkably improved.
According to a preferred embodiment of the present invention, the above-mentioned PIP treatment is performed after a volume ratio of the CVI SiC matrix becomes about 5% or more and about 80% or less.
When the volume ratio is less than 5%, the dense matrices surrounding the ceramic fibers are lessened, and resistance to oxidation is deteriorated. Moreover, when 80% is exceeded, a decrease ratio of Young""s modulus is small, and the resistance to thermal shock cannot sufficiently be enhanced. Therefore, when the volume ratio of the matrix by CVI treatment is set to about 5% or more, about 80% or less, Young""s modulus can sufficiently be reduced and the resistance to thermal shock can remarkably be enhanced as compared with the conventional CMC only by CVI treatment.
Still other objects of the present invention, and the advantageous characteristics thereof, will become apparent from the following description with reference to the accompanying drawings.